Playground surfacing must be reasonably safe for children. The Consumer Product Safety Commission (CPSC) Handbook for Public Playground Safety contains a surface-testing standard called a Maximum Head Injury Coefficient (Max HIC). To properly determine if a surface's HIC meets the Max HIC standard, the surface must be tested in accordance with ASTM F1292-93, Standard Specification for Impact Attenuation of Surface Systems Under and Around Playground Equipment and per ASTM F355-86, Standard Test Method for Shock-Absorbing Properties of Playing Surface Systems and Materials.
As playground surfacing can not be reliably tested in a laboratory, portable field testing equipment is often required, i.e., test equipment that is capable of providing consistent test results in accordance with the CPSC and ASTM standards. To test within these requirements testing personnel employ a linear accelerometer transducer embedded in a metal headform. The testing personnel drop the accelerometer transducer and headform from the specified reference height to the playground surface. Normally electrical wires transmit the raw accelerometer data from the accelerometer transducer to a separate data processing unit which calculates the HIC.
To get consistent reproducible data, the headform must strike the surface in such a way that the linear accelerometer axis is within plus or minus 5 degrees of vertical. Also, the headform must drop from a stationary condition to avoid imparting random accelerations to the headform and skewing the test data. Also, there must be something to support the headform in that stationary condition at varying heights up to 12 feet as specified in ASTM F1292-93.
Current surface-testing systems either use guide elements to guide the headform to impact or comprise hand-released headforms that fall without guidance.
Current systems using flexible guide elements also include some form of rigid support structure that vertically supports the guide elements. Some systems have semi-collapsible support structures, but with rigid guide elements. In any event, all known systems using guide elements either have rigid, non-collapsible support structures or rigid, non-collapsible guide elements. For this reason, these systems are difficult to disassemble, transport and reassemble for field testing.
For example, U.S. Pat. No. 3,426,578 to A. Bergs et al., issued Feb. 11, 1969 discloses an impact testing apparatus for conducting controlled attitude tests. The apparatus includes a drop module, a release means, a pair of guide cables and a support structure that holds the guide elements in a generally vertical orientation. With this design, the test specimen is the drop module rather than the impact surface. The Bergs '578 patent, therefore, includes an impact base positioned on a permanent foundation. Consequently, the Bergs '578 patent's support structure is permanent and not designed for transport.
An example of a transportable system is disclosed in French Patent Number 2,334,096. This patent discloses a portable drop-test device for testing road surfaces with a surface penetrator. The system includes a drop module and a release means. The system has a semi-collapsible support structure with a rigid central guide element. The support structure includes three legs assembled and joined together with cross braces by way of removable wing-nut and bolt fasteners. When unbolted, the support structure is inwardly collapsible onto the rigid guide element much in the same manner as a camera tripod. This allows an operator to reduce the overall diameter of the system for transport, but not its length.
Hand-released headform systems are easy to transport but are difficult to manually release without imparting random translational or rotational loads to the headform. For example, U.S. Pat. No. 4,856,318 issued to Hogan et al. on Aug. 15, 1989 discloses a hand-carried, hand-released transducer module. To comply with ASTM F355-86 an individual must climb a ladder or a piece of playground equipment, then attempt to manually hold the module at the exact reference height and release it without imparting any significant translational or rotational loads.